Dual-projector three-dimensional scanner

ABSTRACT

A current problem with 3D scanners using structured light patterns is choosing a single light pattern to accommodate all possible object/range conditions. Objects far from the 3D scanner often require different patterns than objects that located close to the 3D scanner. In addition, large objects often require different patterns than small objects. To automatically sense and adapt to a wide variety of size/range conditions, the present invention embraces a 3D scanner for dimensioning that has two projectors for projecting two different light patterns. Based on the scanning requirements for a particular object, one of the two projected patterns may be used to obtain information regarding the shape of an object. In one possible embodiment, this shape information is used to obtain the object&#39;s dimensions.

FIELD OF THE INVENTION

The present invention relates to a non-contact measurement system and,in particular, to a structured-light, three-dimensional (3D) scanningsystem that may be used for measuring the dimensions of objects.

BACKGROUND

3D scanning systems (i.e., 3D scanners) are systems that can sense aphysical object (e.g., detect the range/distance of surfaces) in orderto obtain information about the object's shape. 3D scanners may be usedfor a variety of purposes. 3D scanners may serve as the interfacebetween a human and a computing system (e.g., game console). 3D scannersmay also be used to create 3D computer models (e.g., scene restoration).In addition, 3D scanners are important for the non-contact, automaticmeasurement of dimensions that is often required in industry. Forexample, 3D scanners are used in the shipping/freight industry to helpcompute dimensional weight and calculate shipping costs.

3D scanners may use a variety of technologies to sense a physicalobject. Optical sensing is desirable in many circumstances because nophysical contact with the object is required. A structured-light 3Dscanner projects a pattern of light (i.e., light pattern) into a fieldof view. Distortions to the light pattern caused by an object in thefield of view are imaged and analyzed to create a range image, in whicheach pixel has a value that correlates with range (i.e., the distancefrom the 3D scanner to a surface). The range image may be analyzed toobtain the dimensions of the object.

It is common to use a fixed-position, structured-light 3D scanner tomeasure objects that vary in range and in size. Projecting a singlelight pattern imposes limitations on the objects that may bedimensioned. These limitations may prevent the dimensioning of someobjects and/or may slow the dimensioning process (e.g., by requiringsome adjustment). What is more, users of such systems may requiretraining to handle these limitations, thereby undermining the 3Dscanner's advantages of simplicity and automation.

A need exists for a 3D scanner that can dimension a wide variety objectsby automatically sensing and adapting to the different scanningrequirements for each object (e.g., range, size, etc.).

SUMMARY

Accordingly, in one aspect, the present invention embraces adual-projector 3D scanner. The 3D scanner includes a structured-lightprojection subsystem having two projectors: a first projector and asecond projector. The projectors are each configured to project aparticular light pattern onto an object. The first projector projects afirst light pattern, and the second projector projects a second lightpattern. The 3D scanner further includes a camera for capturing imagesof either light pattern reflected from an object. Acomputing-and-control subsystem that is communicatively coupled to thestructured-light projection subsystem and the camera enables the 3Dscanner to obtain information regarding the object's size/shape througha number of process steps. First, the object's scanning requirements areobtained. Next, based on the scanning requirements, either the first orthe second projector is activated, and a pattern image is captured usingthe camera. The resulting pattern image is then processed to produce arange image.

In an exemplary embodiment of the dual-projector 3D scanner, thecomputing-and-control subsystem is configured to analyze the range imageto obtain the object's dimensions.

In an exemplary embodiment of the dual-projector 3D scanner, the firstlight-pattern's pattern-feature density is lower than the secondlight-pattern's pattern-feature density.

In another exemplary embodiment of the dual-projector 3D scanner, thefirst light-pattern's optical intensity is lower than the secondlight-pattern's optical intensity.

In another exemplary embodiment of the dual-projector 3D scanner, thefirst projector's field of view is smaller than the second projector'sfield of view.

In another exemplary embodiment of the dual-projector 3D scanner, theobject's scanning requirements include the object's size.

In another exemplary embodiment of the dual-projector 3D scanner, theobject's scanning requirements include the object's size, and the firstprojector is activated when the object's size is less than about 1 cubiccentimeter, while the second projector is activated when the object'ssize is greater than about 1 cubic meter.

In another exemplary embodiment of the dual-projector 3D scanner, theobject's scanning requirements include the object's range.

In another exemplary embodiment of the dual-projector 3D scanner, theobject's scanning requirements include the object's range, and the firstprojector is activated when the object's is within a range of about 0.5meter to about 2 meters, while the second projector is activated whenthe object's is within a range of about 2 meters to about 4 meters.

In another aspect, the present invention embraces a method fordimensioning an object using a dual-projector three-dimensional (3D)scanner. The method includes activating one of the 3D scanner's twoprojectors to project a light pattern onto the object. Next, the camerais used to capture a preliminary pattern image. At least a portion ofthe preliminary pattern image is then analyzed, and based on theanalysis, one of the 3D scanner's two projectors is selected. The objectis then dimensioned using the selected projector.

In an exemplary embodiment of the method for dimensioning an objectusing a dual-projector three-dimensional (3D) scanner, the object isdimensioned by: (i) activating the selected camera, (ii) capturing apattern image using the camera, (iii) generating a range image from thepattern image, and (iv) deriving the object's dimensions from the rangeimage.

In another exemplary embodiment of the method for dimensioning an objectusing a dual-projector three-dimensional (3D) scanner, the analysis ofthe preliminary pattern image includes determining the object's range.

In another exemplary embodiment of the method for dimensioning an objectusing a dual-projector three-dimensional (3D) scanner, the analysis ofthe preliminary pattern image includes determining the object's size.

In another aspect, the present invention embraces a method fordimensioning an object using a dual-projector three-dimensional (3D)scanner. The method starts with activating a first projector to projecta first light pattern onto the object. Next, a camera is used to capturea first pattern image of the first light pattern reflected from theobject. Next, a second projector is activated to project a second lightpattern onto the object, and a second pattern image of the second lightpattern reflected from the object is captured. The first pattern imageand the second pattern image are evaluated and, based on the evaluation,either the first pattern image or the second pattern image is selected.Finally, the object is dimensioned using the selected pattern image.

In an exemplary embodiment of the method for dimensioning an objectusing a dual-projector three-dimensional (3D) scanner, the object isdimension by generating a range image using the selected pattern imageand then using the range image to derive the object's dimensions.

In another exemplary embodiment of the method for dimensioning an objectusing a dual-projector three-dimensional (3D) scanner, the first patternimage and the second pattern image are evaluated by detecting that, atleast a portion of, the first pattern image or the second pattern imageis saturated.

In another exemplary embodiment of the method for dimensioning an objectusing a dual-projector three-dimensional (3D) scanner, the first patternimage and the second pattern image are evaluated by detecting that theintensity of pattern features, in either the first pattern image or thesecond pattern image, is too low for dimensioning.

In another exemplary embodiment of the method for dimensioning an objectusing a dual-projector three-dimensional (3D) scanner, the first patternimage and the second pattern image are evaluated by detecting that thedensity of pattern features, in either the first pattern image or thesecond pattern image, is too high or too low for dimensioning at orabove a particular accuracy.

In another exemplary embodiment of the method for dimensioning an objectusing a dual-projector three-dimensional (3D) scanner, the first lightpattern's pattern-feature density is lower than the second lightpattern's pattern-feature density.

In another exemplary embodiment of the method for dimensioning an objectusing a dual-projector three-dimensional (3D) scanner, the first lightpattern's optical intensity is lower than the second light pattern'soptical intensity.

In another exemplary embodiment of the method for dimensioning an objectusing a dual-projector three-dimensional (3D) scanner, the firstprojector's field of view is smaller than the second projector's fieldof view.

The foregoing illustrative summary, as well as other exemplaryobjectives and/or advantages of the invention, and the manner in whichthe same are accomplished, are further explained within the followingdetailed description and its accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 graphically depicts an object positioned in front of a 3D scannerat two exemplary positions along a range axis.

FIG. 2 schematically depicts a block diagram of a dual-projector 3Dscanner according to an embodiment of the present invention.

FIG. 3 graphically depicts a flowchart of a method for dimensioning anobject using a dual-projector 3D scanner according to an embodiment ofthe present invention.

FIG. 4 graphically depicts a flowchart of a method for dimensioning anobject using a dual-projector 3D scanner according to an embodiment ofthe present invention.

FIG. 5 graphically depicts a flowchart of a method for dimensioning anobject using a dual-projector 3D scanner according to an embodiment ofthe present invention.

FIG. 6 graphically depicts a flowchart of a method for dimensioning anobject using a dual-projector 3D scanner according to an embodiment ofthe present invention.

DETAILED DESCRIPTION

The present invention embraces a 3D scanner, which may be used for avariety of purposes including dimensioning. Many different technologiesmay be used for 3D scanning. The present invention embraces anon-contact, active 3D-scanner that projects an optical pattern (i.e.,structured light) onto an object and records the reflected pattern as apattern image captured by a digital camera.

The 3D scanner obtains depth information (i.e., range) through the useof a stereoscopically arranged projector and camera. During a rangemeasurement, the projector projects a known light pattern onto asurface. The camera captures an image (i.e., pattern image) of the lightpattern reflected from the object. The reflected pattern will bespatially offset from the known pattern by an amount correlating withthe range of the reflecting object. Analyzing the pattern image forrange can be performed pixel-by-pixel in order to create a range imageof the camera's field of view. Each pixel in the range image has a greyscale value that correlates with range. This range image may be analyzedto derive the dimensions of an object placed in the field of view of the3D scanner.

The 3D scanner's projector projects a light pattern (i.e., pattern) thathas a plurality of pattern elements (i.e., pattern features). Patternfeatures may be regularly spaced (e.g., grid) or randomly spaced.Pattern features may be discreet (e.g., dots) or continuous (e.g.,lines). Pattern features may form repeated patterns or may be locatedrandomly. Pattern features may be distributed over the projected fieldof view uniformly or non-uniformly. Pattern features may be identicallysized, sized according to a group of sizes, or each sized differently.Unless otherwise stated, the present disclosure describes an exemplaryembodiment in which the pattern features are light spots (i.e., dots)that have a similar shape/size and that are randomly distributed overthe projected field of view.

When an object is placed in front of the 3D scanner, it reflects all orsome of the projected light pattern. The portion of the light patternreflected is determined by the 3D scanner's projector, the object'ssize, and the object's range. Dimensioning precision/accuracycorresponds to the number of dots reflected from the object (i.e.,pattern-feature density). Typically, it is important to insure that anobject reflects a sufficient number of dots and that these dots can beimaged accurately by a camera.

Problems with dimensioning can occur when the projected light pattern isnot optimal for an object having a particular size positioned andpositioned at a particular distance from the 3D scanner. A 3D scannerthat projects one pattern may not be able to dimension accurately in allcases.

FIG. 1 graphically illustrates an object 1 placed in two positions infront of a 3D scanner 2. Along a range axis 3, Position “A” 4 is nearthe 3D scanner, while position “B” 5 is far from the 3D scanner. Todimension the object 1, the 3D scanner 2 projects a light pattern (e.g.,pattern of dots) having a field of view 6 that expands as rangeincreases. The object 1 placed in the field of view will reflect aportion of the pattern. The 3D scanner's camera captures a pattern imagethe reflected pattern.

A pattern image of the object located at position “A” 4 will have morereflected dots (i.e., higher pattern-feature density) than a patternimage of the object located at position “B” 5 because the objectintersects more of the projected pattern's field of view 6. Since thefield of view spreads with range, an object placed too close to the 3Dscanner may have areas that do not intersect with the projected pattern.In this case, a light pattern with a larger field of view could helpdimensioning. Alternatively, objects placed too far from the 3D scannermay intersect with the projected pattern insufficiently to allow foraccurate dimensioning. In this case, a light pattern having a smallerfield of view could help dimensioning.

The dots in the pattern image of an object in position “A” will appearlarger than the dots in the pattern image of an object located atposition “B” because the object at position “A” is closer to the 3Dscanner's camera. Objects placed too far from the 3D scanner may havereflected light patterns that are too small to be resolved by the camera(i.e., pixel sampling errors). In this case, a light pattern with largerdots and/or with greater dot spacing could help dimensioning.

The image intensity (i.e., pixel values) of the dots at position “A”will be higher than the image intensity of the dots at position “B”because the object is closer to the 3D scanner. An object placed tooclose to the 3D scanner, may have dot image intensities that saturatethe camera and cause artifacts (e.g., pixel blooming). In this case, alight pattern with a lower intensity could help dimensioning. Objectsplaced too far from the 3D scanner, may have dot image intensities thatare low and do not rise above the noise in the camera'ssensor/electronics (i.e., poor signal-to-noise-ratio (SNR)). In thiscase, a light pattern having a higher intensity could help dimensioning.

The discussion so far has focused on an object having a particular sizethat is positioned both near and far. Similar dimensioning problems mayalso exist for large and small objects located a particular range. Forexample, a large object will intersect more of the projected lightpattern at a particular range than a small object at the same positionand, therefore, may require a larger projected light pattern field ofview. Many possibilities exist because both range and object sizevariations must be accommodated by a 3D scanner.

In some cases, a user may remedy dimensioning problems (e.g., lowaccuracy, no results, etc.) by repositioning the object and/or 3Dscanner. For example, a small object initially placed far from the 3Dscanner may be moved closer to improve dimensioning (e.g., accuracy).Requiring the user to make adjustments or understand the limitations ofthe scanner is not always desirable, and sometimes it is impossible tomake the necessary adjustments due to size and space limitations.Instead, the present invention embraces a system and method foraccommodating the size/range limitations of a 3D scanner automaticallyby adjusting the projected pattern to suit the size/range of an object.

A block diagram of a dual-projector 3D scanner for dimensioning (i.e.,scanner or dimensioner) according to an embodiment of the presentinvention is shown in FIG. 2. The scanner 10 includes a structured-lightprojection subsystem having a first projector 11 and a second projector12. Each projector may include at least one light source (e.g., laserdiode, LED, VCSEL array, etc.). The light source may radiate light at aparticular wavelength or in a band of wavelengths. The light may bevisible or invisible (e.g., infrared). Optics (e.g., filters, lenses,etc.) may be used to condition and project the radiated light. Eachprojector may form a light pattern using a one of a variety oftechnologies. For example, one or more diffractive optical elements(DOE) may be used to create the light pattern.

The first projector 11 projects a first light pattern and the secondprojector projects 12 a second light pattern. The first and second lightpattern may be different in a variety of ways. For example, at aparticular range, the first light pattern's field of view 13 (i.e.,spatial extent of the light pattern) may be smaller than the secondlight pattern's field of view 14. In another exemplary embodiment, thefirst light pattern's pattern-feature density (e.g., the number of dotsin the field of view) may be lower than the second light pattern'spattern-feature density (e.g., dot density). In another exemplaryembodiment, the first light pattern's optical intensity (e.g., opticalpower per dot) may be lower than the second light-pattern's opticalintensity. Other differences between the first and second light patternsmay include (but are not limited to) pattern-feature size,pattern-feature shape, pattern-feature type (e.g., dot, line, etc.),pattern-feature arrangement (e.g., spacing, regularity, etc.),pattern-feature distribution, angular divergence, wavelength, and/orpolarization.

A camera 15 captures a pattern image using a focusing element (e.g.,lens, pinhole, etc.), which forms a real image of the reflected lightpattern onto an image sensor. In some embodiments, the camera mayinclude a filter (e.g., infrared filter), which passes the light patternwhile blocking other (e.g., ambient) light from reaching the sensor. Thecamera's image sensor may convert the real image into an electronicsignal using a plurality of light sensitive elements arranged in acontiguous array, wherein each light sensitive element samples a portionof the camera's field of view 16. The image sensor may use a variety oftechnologies to convert light into electronic signals (e.g., chargecoupled device (i.e., CCD) technology, complementary metal oxidesemiconductor (i.e., CMOS) technology, etc.). Conditioning electronics(e.g., analog-to-digital converters, clocks, amplifiers, digital signalprocessor, etc.) may be included as part of the camera and used tofacilitate the formation of a digital image.

A computing-and-control subsystem 17 is communicatively coupled to thefirst projector 11, the second projector 12, and the camera 15. Thecomputer-and-control subsystem 17 synchronizes operation/timing of theprojectors and the camera (e.g., so that only one projector is on whencamera captures a pattern image). The computer-and-control subsystem 17may also control the camera's settings (e.g. focus, exposure). Thesesettings may be adjusted to correspond with the activated projector, theobject, and/or the environment (e.g., range, ambient lighting, etc.)

The computing-and-control subsystem 17 may include one or moreprocessors 41 (e.g., one or more controller, digital signal processor(DSP), application specific integrated circuit (ASIC), programmable gatearray (PGA), programmable logic controller (PLC), etc.). The processor18 may be configured by processor-executable instructions (e.g.,software) stored in at least one non-transitory storage medium (i.e.,memory) 19 (e.g., read-only memory (ROM), flash memory, a hard-drive,etc.). The processor-executable instructions, when executed by theprocessor 18, configure the 3D scanner to obtain the object's scanningrequirements (e.g., object size/range) and choose either the first orthe second projector based on these requirements. The 3D scanner is thentriggered to capture a pattern image, which is then processed by theprocessor to produce a range image. The range image is then analyzed bythe processor to obtain the object's dimensions. The results of theprocessing and/or analysis may be stored in the computing-and-control'smemory 19.

An exemplary embodiment of a method for dimensioning an object using thedual-projector 3D scanner is shown in FIG. 3. The method begins with oneof the 3D scanner's two projectors projecting a light pattern onto theobject. In the exemplary embodiment shown in FIG. 3, the first projectoris activated 20 initially. While the first projector projects the firstpattern onto the object, the 3D scanner's camera captures a preliminarypattern image 21. The projector settings (e.g., intensity) and camerasettings (e.g., exposure time) used to acquire the preliminary patternimage are typically the same settings used to acquire pattern images fordimensioning. In a possible embodiment, however, the preliminary patternimage may be acquired using different projector/camera settingsconfigured specifically for determining dimensioning requirements.

The preliminary pattern image is analyzed 22 (e.g., by the processorconfigured by software stored in the memory to perform image analysisalgorithms). The results of the analysis include information tofacilitate the selection of one of the two projectors for dimensioning.This information may be related to the object's range/size, the patternquality (e.g., saturation, low signal, object coverage, etc.), ordimensioning accuracy (e.g., pattern-feature density). Based on theanalysis, one of the 3D scanner's two projectors is selected 23 fordimensioning 24.

Dimensioning begins with activating the selected projector 25 to projecta light pattern onto the object. A pattern image of the reflected lightpattern is captured by the camera 26. The pattern image is processed bythe processor to generate a range image 27. Algorithms running on theprocessor analyze the range image to derive the dimension of the object28. These algorithms may also provide the precision and/or accuracy ofthese measurements. In some cases, the algorithms may return ameasurement error when the accuracy of the dimensioning is not within acertain accuracy/precision or when no result can be computed.

Another exemplary embodiment of a method for dimensioning an objectusing the dual-projector 3D scanner is shown in FIG. 4. A firstprojector is activated to project a first light pattern onto an object30. While the projector is activated, a first pattern image is capturedby the camera 31. The first pattern imaged is analyzed using algorithmsrunning on the 3D scanner's processor to determine if the first patternimage is suitable for dimensioning (e.g., estimating dimensioningquality). If the first pattern image is suitable for dimensioning 33,then it processed to generate a range image 34 from which objectdimensions are derived 35. If the first pattern image is not suitablefor dimensioning (e.g., pattern is saturated, pattern is noisy, patternis insufficient to cover object, pattern has a low density on theobject, etc.), then the second projector is activated 36, and a secondpattern image is captured 37. The second pattern image is then analyzed.If the second pattern image is suitable for dimensioning 33, then itprocessed to generate a range image 34 from which object dimensions arederived 35. If the second pattern image is not suitable for dimensioningthen the user may be alerted that dimensioning is not possible 38.

Another exemplary embodiment of a method for dimensioning an objectusing the dual-projector 3D scanner is shown in FIG. 5. In this method,the first projector is activated 40 and a first pattern image iscaptured 41 by the camera. Next, the second projector is activated 42and a second pattern image is captured 43 by the camera. Both the firstand the second pattern images are evaluated 44 (e.g., compared forquality). Based on the results of the evaluation, either the firstpattern image or the second pattern image is selected for dimensioning45. The selected image is then processed to generate a range image 46from which object dimensions are derived 47.

Another exemplary embodiment of a method for dimensioning an objectusing the dual-projector 3D scanner is shown in FIG. 6. In this method,the object is dimensioned using the first projector 50 and dimensionedusing the second projector 51. Then one of the dimensioning results isselected 52. This selection process may include comparing theprecision/accuracy of the two results, and selecting the moreprecise/accurate result.

In summary, the purpose of utilizing two projectors in the 3D scanner isto expand the working limit of the 3D scanner and thus enhance itsperformance. To this end, aspects of the following may be changed: theprojected pattern (e.g., type, angular resolution, feature size, fieldof view, intensity, wavelength, projection direction, etc.); thecamera's settings for a particular projector (e.g., frame rate,resolution, etc.); and the physical arrangement of the camera and eachprojector (e.g., projector/camera spacing, projector/camera orientation,etc.). The present invention envisions any combination of these aspectvariations to enhance 3D scanning performance.

***

To supplement the present disclosure, this application incorporatesentirely by reference the following commonly assigned patents, patentapplication publications, and patent applications:

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In the specification and/or figures, typical embodiments of theinvention have been disclosed. The present invention is not limited tosuch exemplary embodiments. The use of the term “and/or” includes anyand all combinations of one or more of the associated listed items. Thefigures are schematic representations and so are not necessarily drawnto scale. Unless otherwise noted, specific terms have been used in ageneric and descriptive sense and not for purposes of limitation.

The invention claimed is:
 1. A dual-projector three-dimensional (3D)scanner, comprising: a structured-light projection subsystem, comprisinga first projector configured for projecting a first light pattern ontoan object, and a second projector configured for projecting a secondlight pattern onto the object; a camera for capturing pattern images ofthe first light pattern reflected from the object or the second lightpattern reflected from the object; and a computing-and-control subsystemcommunicatively coupled to the structured-light projection subsystem andthe camera, the computing-and-control subsystem configured to: (i)obtain the object's scanning requirements, (ii) activate, depending onthe object's scanning requirements, either the first projector or thesecond projector, (iii) capture, using the camera, a pattern image, and(iv) process the pattern image to produce a range image.
 2. Thedual-projector three-dimensional (3D) scanner according to claim 1,wherein the computing-and-control subsystem is further configured toanalyze the range image to obtain the object's dimensions.
 3. Thedual-projector three-dimensional (3D) scanner according to claim 1,wherein the first light pattern's pattern-feature density is lower thanthe second light pattern's pattern-feature density.
 4. Thedual-projector three-dimensional (3D) scanner according to claim 1,wherein the first light pattern's optical intensity is lower than thesecond light pattern's optical intensity.
 5. The dual-projectorthree-dimensional (3D) scanner according to claim 1, wherein the firstprojector's field of view is smaller than the second projector's fieldof view.
 6. The dual-projector three-dimensional (3D) scanner accordingto claim 1, wherein the object's scanning requirements include theobject's size.
 7. The dual-projector three-dimensional (3D) scanneraccording to claim 6, wherein the first projector is activated when theobject's size is less than about 1 cubic centimeter and the secondprojector is activated when the object's size is greater than about 1cubic meter.
 8. The dual-projector three-dimensional (3D) scanneraccording to claim 1, wherein the object's scanning requirements includethe object's range.
 9. The dual-projector three-dimensional (3D) scanneraccording to claim 8, wherein the first projector is activated when theobject is within a range of about 0.5 meter to about 2 meters and thesecond projector is activated when the object is within a range of about2 meters to about 4 meters.
 10. A method for dimensioning an objectusing a dual-projector three-dimensional (3D) scanner, the methodcomprising: activating one of the 3D scanner's two projectors to projecta light pattern onto the object, capturing, using the camera, apreliminary pattern image, analyzing at least a portion of thepreliminary pattern image, based on the analysis, selecting one of the3D scanner's two projectors, and dimensioning the object using theselected projector; wherein the step of dimensioning comprises:activating the selected projector; capturing, using the camera, apattern image; generating, using the pattern image, a range image; andderiving, using the range image, the object's dimensions.
 11. The methodfor dimensioning an object using a dual-projector three-dimensional (3D)scanner according to claim 10, wherein the step of analyzing comprisesdetermining the object's range.
 12. The method for dimensioning anobject using a dual-projector three-dimensional (3D) scanner accordingto claim 10, wherein the step of analyzing comprises determining theobject's size.
 13. A method for dimensioning an object using adual-projector three-dimensional (3D) scanner, the method comprising:activating a first projector to project a first light pattern onto theobject, capturing, using a camera, a first pattern image of the firstlight pattern reflected from the object, activating a second projectorto project a second light pattern onto the object, capturing, using acamera, a second pattern image of the second light pattern reflectedfrom the object, evaluating the first pattern image and the secondpattern image, selecting, based on the evaluation, either the firstpattern image or the second pattern image, and dimensioning the objectusing the selected pattern image; wherein the step of dimensioningcomprises: generating, using the selected pattern image, a range image;and deriving, using the range image, the object's dimensions.
 14. Themethod for dimensioning an object using a dual-projectorthree-dimensional (3D) scanner according to claim 13, wherein the stepof evaluating comprises detecting that at least a portion of the firstpattern image or the second pattern image is saturated.
 15. The methodfor dimensioning an object using a dual-projector three-dimensional (3D)scanner according to claim 13, wherein the step of evaluating comprisesdetecting that the intensity of pattern features in either the firstpattern image or the second pattern image is too low for dimensioning.16. The method for dimensioning an object using a dual-projectorthree-dimensional (3D) scanner according to claim 13, wherein the stepof evaluating comprises detecting that the density of pattern featuresin either the first pattern image or the second pattern image is eithertoo high or too low for dimensioning at or above a particular accuracy.17. The method for dimensioning an object using a dual-projectorthree-dimensional (3D) scanner according to claim 13, wherein the firstlight pattern's pattern-feature density is lower than the second lightpattern's pattern-feature density.
 18. The method for dimensioning anobject using a dual-projector three-dimensional (3D) scanner accordingto claim 13, wherein the first light pattern's optical intensity islower than the second light pattern's optical intensity.